Spectacle frames exist which are fitted with glass containing liquid crystals. By suitable electronic polarization, such glass can be made opaque or transparent, and can be made to alternate between being opaque and transparent at any desired rate and independently for each eye. Such spectacles can be used for detecting, diagnosing, and treating some anomalies in vision, in particular strabism.
Such high-performance equipment is complex, expensive, and not very suitable for very young children.
Preferred embodiments of the present invention provide apparatus which is simple, very cheap, does not require electronic circuits, and which can be used with very young children even when only a few months' old, for early and reliable detection of troubles with vision, and also for providing effective treatment thereof.